The present invention generally relates to color signal processing apparatus and, more particularly, is directed to a color signal enhancer for use in, for example, a video tape reproducing apparatus.
In U.S. Pat. No. 4,504,853, the teachings of which are fully incorporated herein by reference, there is discussed a color signal enhancer circuit used in a video apparatus such as a video tape recorder (VTR). In the abstract it is stated that the circuit enhances aperiodic transitions occurring in a quadrature modulated subcarrier by deriving a control signal from simultaneously occurring aperiodic transitions in the baseband of the carrier, such as luminance or chrominance, without demodulation of the chroma subcarrier.
Referring to FIG. 1 of the present specification, there is shown an input terminal 1 to which a luminance signal Y separated from a video signal is applied. The luminance signal Y applied to the input terminal 1 is supplied to a horizontal correlation detecting circuit 2.
There is shown an input terminal 3 to which a chroma signal C separated from the video signal is supplied. The chroma signal C applied to the input terminal 3 is supplied to a horizontal correlation detecting circuit 4. In that case, the chroma signal C is a signal modulated by a color subcarrier of 3.58 MHz.
Horizontal correlation detected signals from the horizontal correlation detecting circuits 2 and 4 are supplied to a logic circuit 5. The logic circuit 5 derives a predetermined control signal when a changing point of the luminance component and a changing point of the chroma component coincide with each other. The control signal from the logic circuit 5 is supplied to a modulator 9 which will be described later.
The chroma signal C applied to the input terminal 3 is supplied to a series circuit of first and second delay circuits 6 and 7. The input signal supplied to the first delay circuit 6 and an output signal from the second delay circuit 7 are supplied to a subtracting circuit 8 which generates a difference signal therebetween as a subtracted output. This difference signal is supplied to the modulator 9, in which the difference signal is amplitude by the control signal supplied thereto from the logic circuit 5. The modulated signal from the modulator 9 and the output signal of the first delay circuit 6 are supplied to an adder 10, from which an added signal is supplied to a chroma signal output terminal 11.
A series of waveform diagrams for signals present in this prior art circuit arrangement is illustrated in FIGS. 2A-2G.
In this prior art circuit arrangement, when a chroma signal at a changing point of predetermined colors A and B as shown in FIG. 2A is inputted, the first delay circuit 6 generates a delay signal (see FIG. 2B) and the second delay circuit 7 generates a delay signal (see FIG. 2C). The subtracter 8 subtracts the input signal and the delayed signal by the second delay circuit 7 from each other to generate a differential signal (see FIG. 2D). This differential signal is modulated by the control signal shown in FIG. 2E into a modulated signal (see FIG. 2F) which crosses at a zero crossing point. This modulated signal is added to the output signal of the first delay circuit 6 by the adder 10 so that a chroma signal, which changes rapidly from color A to color B (see FIG. 2G), is developed at the output terminal 11.
As described above, the change of the chroma signal is rapidly carried out, whereby a contour of a reproduced picture is emphasized. Thus, the conventional circuit of FIG. 1 functions as the enhancer.
However, the prior art color signal enhancer is large in scale, complicated in arrangement and very expensive.
Further, in the standard video tape recorder, the chroma signal passes through a bandpass filter a plurality of times upon recording and reproducing so that a characteristic of a reproduced chroma signal finally outputted is disturbed. In other words, if a bandpass filter having rapid characteristic is utilized, group delay characteristics are not uniform so that a so-called overshoot tends to occur behind the zero crossing point of the color signal.